Fluorescent display tubes

ABSTRACT

In a fluorescent display tube of the type comprising an insulator base having a plurality of recesses on one surface thereof which are disposed to form selected patterns to be displayed, a phosphor segment and an electrode contained in each recess and a source of electrons for impinging electrons upon the phosphor elements to cause them to luminesce there is provided a relatively low resistance path directly on the surface of the insulator base for draining electrons impinging upon the surface thereof.

[151 3,705,324 [451 Dec. 5, 1972 United States Patent Masuda I [54] FLUORESCENT DISPLAY TUBES References Cited UNITED STATES PATENTS [72] Inventor: Mitsuru Masuda, Ise, Japan [73] Assignee: ISE Electronics Corporation, lse' Tanji Japan Primary Examiner-John Kominski AttorneyChittick et a1.

22 Filed: Sept. 2a, 1971 l 211 Appl. No.: 183,054

7] ABSTRACT In a fluorescent display tube of the type comprising an insulator base having a plurality of recess 45 84 33 00 88 44 In NH Bk 5s 1 0 s m m" 5 u. a n n n mm 0 n mm m QM m .t mm m a mm Wmh M .Mll r. 55 lb. 0 22 CG .F LL

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SS UI l l] 0 2 3 55 l es on one surface thereof which are disposed to form selected patterns to be displayed, a phosphor segment and an electrode contained in each recess and a source of electrons for impinging electrons upon the phosphor elements to cause them to luminesce there is provided a relatively low resistance path directly on the surface [58] Field ofSearch.....................;..313/1095, 108 R of the insulator base for draining electrons impinging upon the surface thereof.

5 Claims, 6 Drawing Figures P'A'TE'N'TEDBEB 5197.2 3,705,324

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3M 6 ATTORILIEY FLUORESCENT DISPLAY TUBES BACKGROUND OF THE INVENTION This invention relates to a fluorescent display tube and more particularly to a low power type fluorescent tube.

A fluorescent tube generally comprises a base of insulator, for example ceramic, having a plurality of recesses on one surface and a plurality of phosphor segments received in the recesses. FlGpl'of the accompanying drawing shows-a typical construction of a prior art fluorescent tube comprising a ceramic base 1 provided with seven recesses which are arranged generally to form a FIG. 8. In each recess, a phosphor segment 2 is received or embedded as more clearly shown in FIG. 2. Each phosphor segment 2 comprises an anode electrode 2b positioned at the bottom of the recess and provided'vwith a terminal lead 2a extending through the rear surface of the ceramic base 1 and a phosphor 3 covering the surface of anode electrode 2b. A screen grid 4 of metal sheet and provided with a plurality of windows 3 of the number and configuration corresponding to those of phosphor segments 2 is provided to cover the ceramic base. 1. An electron accelerating mesh 5 is provided above the screen grid,4 to cover the entire surface thereof. Accordingly, the electrons emitted from a heaterfi positioned in front of the electron accelerating screen 5 are accelerated and their distribution is made uniform while they pass through electron accelerating mesh 5. Portion of the electrons collide upon the screen grid 4 and are prevented from reaching the ceramic base 1. Remaining portions of the electrons pass through windows 3 to reach phosphor segments 2 to excite phosphors 2c.

. However, with the fluorescent display tube of this type, the percentage of the electrons intercepted by the screen grid 4 is very high so that the value of the screen grid current often amounts to about one-fifth -of the anode current. In other words, since this grid current constitutes a waste current that does not contribute to the excitation of s the phosphors, it is necessary to decrease as far as possible thiswaste current in order to realize a fluorescent tube of low power. For this reason it has beenproposed to eliminate the screen grid 4, as shown in FIG. 3. However, when the screen gridis removed, the electrons that reach the surface of the ceramic base 1 charge negatively the same. Consequently, the electrons projected upon the peripheral portion of each phosphor segment 2 are repelled by the negative charge so that they can not reach the peripheral portions of the phosphor segments 2. In other words, with a previous fluorescent display tube not utilizing a screen grid, the brightness is decreased at the peripheries of respective phosphor segments 2.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved fluorescent display tube of reduced power which can greatly reduce the waste current flowing through the screen grid.

Another object of this invention is to provide an improved fluorescent display tube which is not provided with a screen grid so that it can greatly reduce the waste current but yet increase the brightness of the luminescence of phosphor segments without being affected by the negative charge collected upon the portions of the insulator base about respective phosphor segments.

According to this invention there is provided a fluorescent display tube of the type comprising an insulator base having a plurality of recesses on one surface thereof, the recesses being desposed to form selected patterns to be displayed, a phosphor segment and an electrode contained in each recess, and a source of electrons for impinging electrons upon the phosphor segments to cause them to luminesce, characterized in that there is provided a relatively low resistance path directly on the surface of the insulator base for draining electrons impinging upon the surface thereof.

In one form of'this invention, the low resistance path takes the form of a mask of metal wire net provided with windows corresponding to the phosphor segments anddirectlyapplied on the surface of the insulator ciently drain to ground. the electrons impinging upon the surface of the insulator base.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings FIG. 1 is an exploded perspective view of the principal elements of a prior art fluorescent display tube FIG. 2 is an enlarged sectional view of a portion of the fluorescent display tube shown in FIG. 1

FIG. 3 is a view similar to FIG. 2 but the screen grid has been removed FIG. 4 is an exploded perspective view of an improved fluorescent display tube embodying the invention;

FIG. 5 is an enlarged view of a portion of the display tube shown in FIG. 4 and FIG. 6 is a similar view of a modified embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIGS. 4 and 5 which shows one embodiment of this invention, the fluorescent display tube shown therein comprises a ceramic base 1 having a construction substantially identical to that shown in FIG. 1. Component parts of the display tube corresponding to those shown in FIGS. 1 and 2 are designated by the same reference numerals so it is believed unnecessary to repeat their description.

As shown in FIG. 5, a mask 7 of a fine metal wire mesh is provided directly on the surface of the ceramic base 1. Further, an electron accelerating mesh 5 is disposed at a small distance from the mask 7 to cover the entire surface thereof. It is advantageous to make sufficiently different the mesh sizes of mask 7 and electron accelerating mesh 5 for the purpose of preventing an interference therebetween. As shown by dotted With this improved construction, electrons emitted from heater 6 positioned in front of the electron accelerating mesh are accelerated and their distribution is made uniform while they pass through the electron accelerating mesh 5. Portions of the electrons are permitted to reach some of the phosphor segments 2 which are maintained at a high potential at that time to excite phosphors 2c on these selected phosphor segments whereas remaining portions of the electrons are caused to impinge directly upon the surface of the ceramic base 1 just in the same manner as has been described hereinabove in connection with FIG. 3. In the improved fluorescent tube, however, since the mask 7 of a metal wire mesh is mounted directly upon the surface of the ceramic base 1, electrodes colliding upon this surface will be drained to the ground. In other words, the mask 7 provides a low resistance grounding path for the colliding electron, thus efficiently preventing them from negatively charging the surface of the ceramic base 1 thereby ensuring uniform luminescence over the entire areas of respective phosphor segments 2. Further, the improved mask of a metal wire mesh collects much smaller quantity of the waste current than the conventional screen of metal plate. For this reason the efficiency of the fluorescent display tube can be greatly improved and the power consumption can also be decreased greatly.

In the modified embodiment shown in FIG. 6 the construction of the fluorescent display tube is much simplified by eliminating the screen of metal sheet shown in FIG. 1 and the mesh of metal wire net shown in FIGS. 4 and 5. In this embodiment, the low resistance grounding path for the colliding electrons is provided by using a relatively low resistivity ceramic base 1 having a conductivity of the order of about 3 X10 to 10 ohm-cm. Such a low resistivity ceramic base can be readily preparing by firing a mixture of a ceramic raw material and a small quantity of an electroconductive material. Although described as having a low resistivity, the resistivity of the ceramic base I is much higher than that of metal or ordinary conductor so that it is possible to maintain the potential impressed upon respective phosphors 2c or anode electrodes but the electrons impinging upon the surface of the ceramic base can efficiently be drained to the ground through the ceramic body.

While the invention has been shown and described in terms of some preferred embodiments thereof it will be clear that many changes and modification will be obvious to one skilled in the art without departing the scope of the invention as defined in the appended claim.

What is claimed 1. In a fluorescent display tube of the type comprising a insulator base having a plurality of recesses on one surface thereof, said recesses being disposed to form selected patterns to be displayed, a phosphor segment and an electrode contained in each of said recesses, and a source of electrons for impinging electrons upon said phosphor segments to cause them to luminesce, the improvement which comprises a relatively low resistance path provided directly on the surface of said insulator base for draining said electrons imaging upon the surface thereof.

2. The fluorescent display tube according to claim 1 wherein said low resistancepath is formed by a maskof metal wire net directly applied on the surface of said insulator base.

3. The fluorescent display tube according to claim 1 wherein said insulator base has a conductivity of about 3 X 10 to 10 ohm-cm at room temperature whereby to provide said low resistance path.

4. The fluorescent display tube according to claim 2 wherein said mask is provided with windows corresponding to said phosphor segments.

5. The fluorescent display tube according to claim 2 wherein said display tube is provided with an electron accelerating mesh located between said source of electrons and said mask. 

1. In a fluorescent display tube of the type comprising a insulator base having a plurality of recesses on one surface thereof, said recesses being disposed to form selected patterns to be displayed, a phosphor segment and an electrode contained in each of said recesses, and a source of electrons for impinging electrons upon said phosphor segments to cause them to luminesce, the improvement which comprises a relatively low resistance path provided directly on the surface of said insulator base for draining said electrons imaging upon the surface thereof.
 2. The fluorescent display tube according to claim 1 wherein said low resistance path is formed by a mask of metal wire net directly applied on the surface of said insulator base.
 3. The fluorescent display tube according to claim 1 wherein said insulator base has a conductivity of about 3 X 105 to 108 ohm-cm at room temperature whereby to provide said low resistance path.
 4. The fluorescent display tube according to claim 2 wherein said mask is provided with windows corresponding to said phosphor segments.
 5. The fluorescent display tube according to claim 2 wherein said display tube is provided with an electron accelerating mesh located between said source of electrons and said mask. 